微纤形态结构对PP/PA66原位微纤复合材料流变性能的影响

利用三角形排列三螺杆挤出机(triangle arrayed triple-screw extruder,TTSE)低温原位拉伸直接挤出制备了聚丙烯/聚己二酰己二胺(PP/PA66)原位微纤复合材料.通过三螺杆挤出机内部高强度的剪切-拉伸流场,研究了不同工艺参数如PA66含量、加工温度和螺杆转速下原位微纤复合材料中纤维的直径和长径比,并分析微纤长径比对复合材料动态流变性能的影响,且着重探究微纤长径比对凝胶点形成的影响.形貌分析结果显示,工艺条件极大地影响了微纤形貌,且PA66微纤长径比随分散相含量和螺杆转速的提高逐渐增加;动态流变数据说明,随着微纤长径比的增加,复合材料低频下的储能模量明显提高且比纯PP要高,同时,低频下的损耗角正切值降低且变化趋于平缓,而Cole-Cole圆半径显著增大,此时微纤复合材料表现出类凝胶的流变行为;原位微纤自缠结形成凝胶网络,微纤长径比越大,形成临界凝胶网络所需的PA66微纤含量越低,当长径比为210时,形成凝胶点时微纤含量仅3.80 wt%.

Effect of Fibrillar Morphology on the Rheological Properties of Polypropylene/Poly(hexamethylene adipamide) in situ Microfibrillar Composites

The blending of immiscible polymers has emerged as an effective tool to control the rheological properties of the outcome polymer composite.The properties of the immiscible polymer blends are closely related to their morphology.In situ fibrillation of dispersed phase has been prepared during polymer blending through complex shear and extensional flow,coalescence of dispersed phase domains.In this paper,polypropylene/ poly(hexamethylene adipamide) (PP/PA66) in situ microfibrillar composites were prepared by direct extrusion through triangle arrayed triple-screw extruder (TTSE) at low temperatures between the melting points of the two phases.The microfibrillar morphology was adjusted and controlled through changing the PA66 content and processing parameters (temperature and screw speed).The fibrillar aspect ratio increased with PA66 content and the screw speed,owing to better dispersed phase to coalescence and stronger shear and extensional flow.The effect of fibrillar morphology on the rheological properties of PP/PA66 composites was investigated.The results showed that the dynamic storage modulus of microfibril composites at low frequency were apparently higher than that of PP and increased with the fibrillar aspect ratio.Furthermore,the slope of the double logarithmic plot of G'versus ω at lower frequence decreased with the increase in the fibrillar aspect ratio.At the same time,the loss tangent tanδ value decreased and the plots of Cole-Cole circle radius increased with increased fibrillar aspect ratio.This indicated that the system exhibited the characteristics of a pseudo-solid or gel.The presence of a fibrillar network defined by topological (entangled) interactions was expected to create additional and large contributions to the viscoelasticity of the polymer matrix.A multi-frequency plot of tanδ versus the fibril content (Winter-Chambon criteria) was used to reveal the gel point of composite system with different fibrillar morphology.The results showed that the critical gel point was decreased with the fibrillar aspect ratio due to enhanced interconnected microstructures.